On the subject of roofing your run, while it may not be necessary to keep foxes out, if your fencing is tall enough, a roof is very handy to save you from feeding the entire squirrel population of your new neighbourhood! Ours is about 6'3" high, to allow my husband to walk around without crouching.

Chickens are a girl's best friend (though diamonds would be nice too!)

25m fencing kit with energiser is about £200 depending on where you get it from and the quality - whether its got a gate in it, colour and make etc. a leisure battery is about £100 (have to replace every 4 years or so I believe) or if running off mains, the lead is about £25 so the cheaper way to power it.
I'd get a piece of rope and measure the area out before committing to buying though, as a lot of companys wont let you return net once its been unravelled.